Phosphoinositides. 1. Configuration of the inositol phosphate in liver phosphatidylinositol

Abstract

INSULIN AND AMINO ACID ACCUMULATION 495 in certain ['4C]amino acids has been investigated, together with the effect of insulin thereon. No important differences between the behaviour of the cut and intact preparations was observed. 2. With alanine, m-aminoi8obutyric acid, glycine, leucine, lysine, ornithine and phenylalanine the ratio of concentration of radioactivity in tissue water to that in the medium exceeded unity. With glutamic acid and aspartic acid the ratio was below unity, probably because of the rapid metabolism of these amino acids in isolated rat diaphragm. 3. The addition of insulin to the medium significantly raised the ratio for glycine and m-aminoi8obutyric acid, but not for the other amino acids under study. The effect ofinsulin was similar whether or not glucose was added to the medium. It was abolished by anoxia and by cooling the system to 120. 4. Under anoxic conditions, both in the presence or absence of insulin, the ratio was significantly raised by the addition of glucose to the medium. A similar effect of glucose was not seen under any other conditions studied. 5. No substantial evidence has been obtained to suggest that insulin promotes the incorporation of amino acids into protein in isolated diaphragm by enhancing the rate of entry of amino acids into the cytoplasm of the cells from the medium. This work has been greatly helped by a generous grant from the British Diabetic Association for the purchase of radioactive amino acids.

Role of Phospholipids in Endocytosis, Phagocytosis, and Macropinocytosis

“…Phosphatidylinositol (PtdIns), formerly called monophosphoinositide (152), comprises a sizable fraction (10 -15%) of the cellular phospholipids (375). PtdIns, an anionic phospholipid, is present in various organelles and, like the aminophospholipids, it is much more abundant in the inner leaflet of the plasmalemma than in the outer leaflet (91).…”

Biosynthesis of phosphoinositol-containing sphingolipids from phosphatidylinositol by a membrane preparation from Saccharomyces cerevisiae

“…a To a sample of the alkali-stable products (1,480 32P cpm) prepared as indicated in the legend to Fig. 1 and isolated by preparative thin-layer chromatography on a PLQ-1000 silica gel plate, using the solvent CHC13-CH30H-4.2 N NH40H (9:7:2, vol/vol), was added authentic glycerophospho[14C]inositol (8,075 '4C cpm). The mixture was hydrolyzed in aqueous 1.0 N KOH at 37°C for 15 h as described previously (16).…”

Phosphoinositides. 2. The inositol 1-phosphate structure in liver phosphatidylinositol

“…Alkaline hydrolysis of phosphatidylinositol or glycerylphosphorylinositol gives a mixture of inositol monophosphate and glycerophosphate in proportions suggesting that the inositol of the original lipid is phosphorylated in the 1or 2position (Hawthorne, 1960). Paper chromatography of such hydrolysates shows the presence of inositol 1-and 2-phosphate.…”

“…Phospholipids. Liver phosphatidylinositol was prepared as described by Hawthorne (1960). Crude groundnut phosphoinositide, which is similar to the soya-bean product, was also made by the method of Hawthorne (1955).…”